Cross-reference to Related Applications

This application claims priority to US App. Ser. No. 62/118,224, filed February 19, 2015, and incorporated herein by reference.

Field

The present invention relates to saw blades and processes for making same. Background

It is known for saw blades, such as those for use with oscillating saws, to be made of two materials. Often a harder material is used for the saw teeth and a lower- cost material is used for the bulk of the saw blade.

FIG. 12 shows an example of such a saw blade 200. The saw blade includes a main plate 202, which attaches to the saw, and another plate 204 that carries cutting teeth. The plates 202, 204 are attached at a single straight joint 206. The straight joint 206 is susceptible to crack propagation. The geometry alone may cause premature failure of the saw blade 200 to result, including complete separation of the plates 202, 204. This problem is magnified when an embrittling joining technology is used to join the plates 202, 204. Hence, it is common to heat treat whole saw blades 200 after the plates 202, 204 are joined, as well as perform other treatments (e.g., coatings) on whole saw blades 200. However, treating entire saw blades 200 can be very inefficient, as space within treatment fixtures is consumed by the relatively larger main plate 202 which often does not actually require any or the same level of treatment as the cutting teeth. In short, the use of a straight joint to attach cutting teeth to bulk material is problematic and leads to blade failure. Further, potential solutions within the state-of-the-art require increased manufacturing complexity and cost.

Summary

According to one aspect of the present invention, a saw blade includes a backing plate and a toothed plate. The toothed plate includes a plurality of cutting teeth for cutting into material and defining a cutting plate. The toothed plate is permanently joined to the backing plate along a non-straight joint in the cutting plane.

The toothed plate can include a joint edge having a convexly curved portion that is fit into a concavely curved portion of a joint edge of the backing plate.

The toothed plate can include a tongue that mates with a complementary recess in the backing plate to form the non-straight joint.

The tongue can be U-shaped.

The tongue can be V-shaped. The non-straight joint can be perpendicular to an outside edge of the saw blade at the outside edge of the saw blade.

An extent of the non-straight joint can be aligned at a predetermined acute angle to an outside edge of the saw blade at the outside edge of the saw blade. The backing plate and the toothed plate can include a protruding cratering tab located at an extent of the non-straight joint.

The toothed plate can be made of a harder material than the backing plate.

The toothed plate can be made of high-speed steel and the backing plate can be made of a different class of steel. The toothed plate can be coated when the backing plate is not coated.

The non-straight joint can include laser- welded material.

The non-straight joint can include electron beam- welded material.

The non-straight joint can include brazing material.

The length of the toothed plate can be between about io% and about 40% of a total length of the saw blade as extending from an axis of oscillation to the cutting teeth.

In accordance with another aspect of the present invention, a process for manufacturing a saw blade can include permanently joining a toothed plate to a backing plate along a non-straight joint, the non-straight joint in a cutting plane defined by the toothed plate.

The process can further include fitting a joint edge of the toothed plate having a convexly curved portion into a concavely curved portion of a joint edge of the backing plate so as to prepare the non-straight joint for permanent joining.

The process can further include mating a tongue of the toothed plate with a complementary recess in the backing plate so as to prepare the non-straight joint for permanent joining. The process can further include seating a flat of the toothed plate against a complementary flat of the backing plate to align the toothed plate with the backing plate as part of preparing the non-straight joint for permanent joining.

Permanently joining the toothed plate to the backing plate can include thermally joining the toothed plate to the backing plate. Thermally joining can include laser welding.

Thermally joining can include electron beam welding.

Thermally joining can include brazing.

The process can further include heat treating the toothed plate before permanently joining the toothed plate to the backing plate.

The process can further include coating the toothed plate before permanently joining the toothed plate to the backing plate.

Brief Description of the Drawings

The drawings illustrate, by way of example only, embodiments of the present invention.

FIG. l is a perspective view of an oscillating saw with attached saw blade according to an embodiment of the present invention.

FIG. 2 is a plan view of the saw blade. FIG. 3 is an exploded plan view of a portion of the saw blade.

FIG. 4 is a plan view of a saw blade having a V-shaped joint according to another embodiment of the present invention.

FIG. 5 is a plan view of a saw blade having cratering tabs according to another embodiment of the present invention. FIGs. 6 - 10 are partial plan views of non-straight joints according other embodiments of the present invention.

FIG. 11 is a flowchart of a process for manufacturing a saw blade according to the present invention. FIG. 12 is a plan view of a prior art saw blade.

Detailed Description

Described herein are various saw blades and processes for making same to solve at least some of the problems of state-of-the-art blades discussed above. Each saw blade described herein has a toothed plate permanently joined to a backing plate along a non-straight joint. Various non-straight joints are discussed. Advantages of the present invention may include increased blade strength, easier

manufacture, and reduced manufacturing time and cost.

FIG. l shows an oscillating saw 10 with a saw blade 12 according to an

embodiment of the present invention. The oscillating saw 10 may be electrically powered and maybe of the kind used in the construction industry. The oscillating saw 10 may include an electric motor and gearing mounted within an outer housing. An on/off switch, oscillation frequency control, power cord, battery, depth stop, suction device for collecting cuttings, as well as other components may also be provided. The techniques discussed herein can be used with other types of saw blade and other types of saws.

A hub 14 extends from the oscillating saw 10 and rotates about an axis of oscillation O in an oscillatory manner during operation of the saw 10. Depending on the specific saw 10, the hub 14 may oscillate through about three to five degrees of angular span at a frequency of about 30,000 oscillations per minute. Naturally, these numbers are merely examples and other angular spans and frequencies are also contemplated.

The saw blade 12 includes a shank 16 that is removably connectable to the hub 14 by way of, for example, fasteners such as one or more screws or bolts, a clamp, and the like. The saw blade 12 further includes a backing plate 20 and a toothed plate 22. The backing plate 20 and toothed plate 22 together form a generally flat plate, and the toothed plate 22 defines a cutting plane through which the blade 12 oscillates during a cut.

The backing plate 20 is fixed to the shank 16 by resistance spot welding, shown at 18. Alternatively, the backing plate 20 can be fixed to the shank 16 by Gas Tungsten Arc Welding (GTAW), brazing, soldering, cementing, using an adhesive, screwing/bolting, or similar. Equally, the backing plate 20 and shank 16 may be formed from a unitary piece of material.

The toothed plate 22 includes a plurality of cutting teeth 24 arranged in an arcuate tooth pattern. The arcuate tooth pattern follows a circular arc that is centered at about the axis of oscillation O. Such centering is approximate and minor variations can be tolerated provided that any resulting hammering can also be tolerated. Alternatively, the plurality of cutting teeth 24 can be arranged in another pattern, such as a straight line. During operation, after the shank 16 of the saw blade 12 is attached to the saw 10, the saw is powered and the blade 12 oscillates about the axis O causing the arcuate arrangement of cutting teeth 24 to follow an oscillating path M. Then, the saw 10 is manually pushed in direction C, thereby causing the blade 12 to cut into the target material, which can include materials such as wood, synthetic materials, water pipe, sheet metal, and fasters (e.g., screws, nails, etc.) attached to or embedded within such materials. Precise and efficient plunge cuts, in which the saw blade 12 enters the material perpendicular to the surface of the material, can thereby be performed.

FIG.2 shows the saw blade 12 removed from the saw 10. The saw blade 12 has a planar front surface, shown, and a planar rear surface, opposite. Each of the planar front and rear surfaces, and any plane there-between, can be considered the cutting plane. It is understood that a volume of material is removed during a cut, and the term "cutting plane" is used herein merely as a convenience. Further, the terms front and rear are used herein for sake of explanation and are not intended to be limiting to any particular orientation. The same applies to other directional terms such as right, rightwards, left, leftwards, top, bottom, and the like.

The arcuate arrangement of cutting teeth 24 may be configured to face outwardly on opposite sides of a longitudinal centerline Z of the saw blade 12. That is, teeth on the left size of centerline Z cut when the blade moves leftwards, and teeth on the right size of centerline Z cut when the blade moves rightwards. Other teeth configurations and shapes may be used.

The toothed plate 22 is permanently joined to the backing plate 20 along a non- straight joint 26 whose non-straight path lies in the cutting plane of the blade 12. The path of the non-straight joint 26 can include one or more curves, one or more lines, or some combination of such. The only paths specifically excluded are a single straight path and single arcuate path centered at or near the axis of oscillation O. Suitable paths within the scope of this invention, in addition to those disclosed herein, will be apparent to those of ordinary skill in the art given the benefit of this disclosure. The toothed plate 22 is made of a harder material than the backing plate 20. In this embodiment, the toothed plate 22 is made of high-speed steel (HSS), sintered carbide, or similar, and the backing plate 20 is made of a different class of steel, such as steels commonly known as carbon steel, alloy steel, low-alloy steel, mild steel, or similar. Further, the toothed plate 22 can be coated to increase hardness and reduce friction, while the backing plate 20 need not be coated at all or need not be coated to the same degree.

In this embodiment, the toothed plate 22 is permanently joined to the backing plate 20 at a weld 28 (region between the dashed curves) that forms the non- straight joint 26. More particularly, in this embodiment, laser welding is used to weld the toothed plate 22 to the backing plate 20 and consequently the weld 28 includes laser-welded material. In other embodiments, other thermal joining processes can be used and the permanent joint can include electron beam-welded material, brazing material, or similar.

The non-straight joints discussed herein, of which the joint 26 is but one example, have increased strength over single straight paths, in that a straight easy break axis is avoided. This is particularly the case when embrittling joining processes, such as laser welding, are used. Further, the non-straight joints discussed herein avoid the use of sharp corners, which reduces or eliminates stress risers.

Various non-straight joint paths maybe used. However, the distance H from the end of the cutting teeth 24 to the extents of the non-straight joint 26 should be made as small as practical. This reduces the force acting on the extents of the non-straight joint 26 due to a bending moment acting on the blade caused by resistance of the material being cut, where such force may induce cracking in the relatively brittle weld 28. Practically speaking, this makes non-straight joint paths that have ends starting closer to cutting teeth 24 and central areas more distant from the cutting teeth 24 a stronger and therefore preferable choice. In other words, increased bending moments are more tolerable in the material of the backing plate 20, as opposed to the more brittle material of the toothed plate 22 and weld 28. This in mind, the overall size of the toothed plate 22 can be minimized by reducing distance H, while still maintaining enough size for process and handling considerations, such as stamping, machining, coating, heat treating, and similar. In various embodiments, the distance H can be selected to range from about 10% of the total length of the saw blade 12 to about 40% of the total length.

With reference to FIG. 3, which shows the toothed plate 22 and backing plate 20 prior to being permanently joined, the toothed plate 22 includes a joint edge 30 having a convexly curved portion 32 that is shaped to fit into a concavely curved portion 34 of a joint edge 36 of the backing plate 20. In other words, the toothed plate 22 includes the male portion and the backing plate 20 includes the female portion of the joint 26. In the embodiment depicted, the toothed plate 22 includes a tongue 40 that extends towards the axis of oscillation O and mates with a complementary recess 42 in the backing plate 20 to form the non-straight joint 26. More specifically, the tongue 40 is U-shaped. In other embodiments, one or more convexly curved portions 32 of the toothed-plate joint edge 30 and one or more complementary- shaped concavely curved portions 34 of the backing-plate joint edge 36 may be used.

In various embodiments, the depth D of the tongue 40, the median width L of the tongue 40, and the overall width W of the blade 12 at the location of the joint 26 can be selected to conform to various proportions. For instance, the depth D may be selected to be between about 25% and about 75% of the median width L of the tongue 40. The median width L of the tongue 40 may be selected to be between about 25% and about 75% of the overall width W of the blade 12. In the example shown, the depth D of the tongue 40 is about 50% of its median width L, which in turn is about 50% of the overall width W of the blade 12. This can advantageously increase the strength of the joint 26. In various embodiments, the shape of the path of the non-straight joint 26 can be selected to conform to minimum and maximum radiuses, such as about 0.07 inches (1.8 mm) minimum radius and about 0.40 inches (10. 2 mm) maximum radius. More specifically, the minimum and maximum radiuses can be selected as about 0.09 inches (2.3 mm) minimum radius and about 0.25 inches (6.4 mm) maximum radius. This can advantageously increase manufacturability.

The tongue 40 and complementary recess 42 are advantageously readily machinable shapes that, when permanently joined offer suitable strength and crack resistance. More complex shapes can be used, provide that any resulting additional machining complexity or difficulty can be tolerated. In this embodiment, each of the extents of the non-straight joint 26 is

perpendicular to the respective outside edge 50 of the saw blade at a location adjacent or near the outside edge 50 of the saw blade. Complementary flats 52, 54 of the joint edges 30, 36 are provided, resulting in each of the extents of the non-straight joint 26 being straight in these regions. The flats 52, 54

advantageously assist in seating the toothed plate 22 to the backing plate 20 and properly aligning oscillating path M of the cutting teeth 24 with the axis of oscillation O. The flats 52, 54 may range in length along the length of the path from about 0.04 inches (1 mm) to about 0.20 inches (5 mm) or longer. In other embodiments, only one extent of the non-straight joint 26 has such

complementary flats. FIG. 4 shows another embodiment of a saw blade 60 according to the present invention. The saw blade 60 is substantially the same as the saw blade 12

discussed above, and only differences will be discussed in detail. Features and aspects of the saw blade 12 can be used with the saw blade 60 without departing from the scope of the present invention. The saw blade 60 includes a backing plate 62 and a toothed plate 64

permanently joined at a non-straight joint 66. The non-straight joint 66 follows a path that defines a V-shaped tongue 68 in the toothed plate 64 and

complementary recess in the backing plate 62. The non-straight joint 66 includes straight segments on both sides of a curved segment. At least one extent 70 of the non-straight joint 66 is aligned at a predetermined acute angle A to an outside edge 72 of the saw blade 60 at the location where the extent terminates at the outside edge 72. In this embodiment, both extents 70 of the non-straight joint 66 are constrained in this way. The non-straight joint 66 emerging from the outside edge 72 at angle A may help reduce or eliminate end- of -weld cratering, particularly when laser welding is used to complete the non- straight joint 66. The acute angle A can be limited to a maximum of about 75 degrees, and maybe of reverse orientation (see angle B of FIG. 6).

FIG. 5 shows another embodiment of a saw blade 8o according to the present invention. The saw blade 8o is substantially the same as the saw blade 12

discussed above, and only differences will be discussed in detail. Features and aspects of the saw blade 12 can be used with the saw blade 80 without departing from the scope of the present invention.

The saw blade 80 includes a backing plate 82 and a toothed plate 84

permanently joined at a non-straight joint 86.

The backing plate 82 includes a cratering tab 88 at each extent of the non- straight joint 86. Each cratering tab 88 protrudes from the respective outside edge 90 of the backing plate 82. Similarly, the toothed plate 84 includes a cratering tab 92 at each extent of the non-straight joint 86. Each cratering tab 92 protrudes from the respective outside edge 94 of the toothed plate 84. Adjacent cratering tabs 88, 92 are fused together during laser welding of the non-straight joint 86 and provide a spot for cratering that may occur when the laser enters or exits the base material. The cratering tabs 88, 92 maybe removed by machining, grinding, laser cutting, or similar process after welding is complete. This can advantageously remove craters from the finished saw blade 80, as such craters may act as stress risers. In this embodiment, four cratering tabs 88, 92 are provided. In other embodiments, one or more of the cratenng tabs 88, 92 can be provided at one or more locations where cratering is expected and cannot be tolerated. That is, not all four of the cratering tabs 88, 92 need be provided.

The number, positioning, and size of any cratering tabs 88, 92 provided can be selected to reduce or eliminate the need to remove any remaining material of the cratering tabs 88, 92 after welding is complete. It is contemplated that cratering tab material may flow back into the crater and provide a low or near zero stress riser. Hence, cratering tabs 88, 92 can be selected to be nearly or entirely consumed by the crater. In designs where a cratering tab cannot be practically made to be consumed by the crater, the number, positioning, and size of any cratering tabs 88, 92 provided can be selected so that the material remaining from the cratering tabs 88, 92 acts as a stress reducer. That is, the post-weld cratering tabs 88, 92 compensate for the stress riser effect of the crater itself. Whether the cratering tabs are configured to be removed by the crater or to compensate for a stress riser effect of the crater, it is advantageous that it may be unnecessary to remove cratering tabs after welding.

FIGs. 6 through 10 illustrate additional embodiments according to the present invention. The saw blades of these embodiments are substantially the same as the saw blade 12 discussed above, and only differences will be discussed in detail. Features and aspects of these embodiments can be combined with features and aspects of the saw blades discussed above, without departing from the scope of the present invention.

FIG. 6 shows a non-straight permanent joint 100 having extents of reversing curvature. The extents of the non-straight joint 100 emerge from the edges of the blade at an acute angle B, which is oriented opposite the angle shown in FIG. 4. The orientation of angle B maybe selected to reduce or eliminate cratering, or, if cratering cannot be avoided, to cause cratering to tend to occur on the material most able to withstand the resulting stress riser. It is contemplated that the less hard material of the backing plate is better suited to absorb any end-of-weld cratering that may occur. Hence, the orientation of angle B, as well as the specific value of the angle B, can be selected to bias cratering towards the backing plate. The acute angle B can be limited to a maximum of about 75 degrees.

Various material combinations and thermal joining processes may have better cratering results based on whether an acute angle A or an acute angle B is selected for the extents of the non-straight joint. It is contemplated that selecting a suitable angle A or B for a particular blade design is within the ability of the person of ordinary skill given the benefit of this disclosure.

FIG. 7 shows a non-straight permanent joint 102 that is not symmetric about the longitudinal centerline of the saw blade. While it is contemplated that symmetric non-straight joints are preferable, the symmetry of the non-straight joints described here is not particularly limited. FIG.8 shows a non-straight permanent joint 104 having relatively long flats, as compared to the flats discussed above with respect to FIG.3.

FIG.9 shows a non-straight permanent joint 106 defining several fingers or tongues and complementary recesses in the backing and toothed plates. FIG. 10 shows a non-straight permanent joint 108 made up of a plurality of individual straight segments. Although the entirety of each joint discussed herein is not straight, such a joint may include or be completely made of straight segments.

FIG. 11 shows a process for manufacturing a saw blade, such as any of the saw blades discussed herein. The process includes steps to make the toothed plate, separate steps to make the backing plate, and steps to permanently join the toothed plate and the backing plate.

Step 120 includes manufacturing a blank for the toothed plate. This can include stamping plate material in a die or similar process. A shaving die, a coining or cold-forging die, or similar die may be used. Such dies may beneficially provide a finished or near finished joint edge. Surfaces of the toothed plate blank may then be ground to final size and approximate surface finish, which can include use of double-disc grinding or other type of surface grinding. Fine blanking or broaching may be used, and such may beneficially provide a finished or near finished joint edge. Next, step 122 includes finishing the joint edge of the toothed plate by a machining operation such as milling, for example, to facilitate a substantially gapless connection to the complementary edge of the backing plate. The toothed plate may then be gently deburred by tumbling, vibratory deburring, or similar process. Step 122 need not be performed if step 120 provides a suitably finished joint edge.

Step 124 subsequently includes machining cutting teeth into the toothed plate blank by, for instance, milling, broaching, or similar operation. The tooth set is then created by a stamping, bending, or coining process using a die. Then, at step 126, the toothed plate is cleaned to reduce or prevent

contamination during subsequent processes.

Next, step 128 includes loading a plurality of toothed plates into one or more heat-treating fixtures and then heat treated to a hardness of not less than about Rockwell C scale 60. Other hardness values may also be suitable, depending on service requirements for the saw blade. Heat treating can be performed in a vacuum oven to prevent or reduce the creation of oxide scale, which may interfere with the subsequent laser-welding process.

Subsequently, step 130 maybe performed. Step 130 includes loading the heat- treated plurality of toothed plates into one or more fixtures for a coating process, such as physical vapor deposition (PVD), to increase hardness and reduce cutting friction of the toothed plates.

It is noteworthy that heat treating and coating, if performed, are done before joining the toothed plate to the backing plate. That is, welding or other thermal joining process is performed after heat treating and coating, if performed. It is an advantage of the present invention that part density of toothed plates within known heat-treating and coating fixtures can be increased, as the toothed plates are relatively small when compared to entire saw blades. This is made possible, at least in part, by use of the non-straight joint, discussed above, and the resulting relatively small size of the toothed plates. At the same time, the non- straight joint maintains suitable service strength of the attachment of the toothed plate to the backing plate. Suitable strength maybe maintained even in the absence of post-weld heat treatment. This increased part density with the same or better joint strength allows the present invention to increase production rates and reduce costs. Step 140 includes manufacturing a blank for the backing plate. This can include stamping plate material in a die or similar process. A shaving die, a coining or cold-forging die, or similar die maybe used. Such dies may beneficially provide a finished or near finished joint edge. Fine blanking or broaching maybe used, and such may beneficially provide a finished or near finished joint edge. Next, step 142 includes finishing the joint edge of the backing plate by a machining operation such as milling, for example, to facilitate a substantially gapless connection to the complementary edge of the toothed plate. The backing plate may then be gently deburred by tumbling, vibratory deburring, or similar process. Step 142 need not be performed if step 140 provides a suitably finished joint edge.

Step 144 subsequently includes loading a plurality of backing plates into one or more heat-treating fixtures and then heat treated to a hardness of between about Rockwell C scale 15 to about Rockwell C scale 45. Other hardness values may also be suitable, depending on service requirements for the saw blade. Heat treating can be performed in a vacuum oven to prevent or reduce the creation of oxide scale, which may interfere with the subsequent laser-welding process.

After batches of toothed plates and backing plates are prepared, as described, above, step 150 includes fitting a joint edge of a toothed plate to a joint edge of a backing plate, so as to prepare the non-straight joint for permanent joining. Depending on the selected shape of the non-straight joint, this can include mating a tongue of the toothed plate with a complementary recess in the backing plate. Complementary flats on the toothed plate and the backing plate may be seated against one another to properly align the toothed plate with the backing plate. A fixture can be used to temporarily hold the toothed plate and the backing plate together.

Then, step 152 includes permanently joining the toothed plate to the backing plate along the non-straight joint. Permanently joining the toothed plate to the backing plate includes thermally joining the toothed plate to the backing plate by, for example, laser welding. Multiple passes maybe required for suitable penetration and both sides of the joint may have to be welded. Alternatively, other suitable thermal j oining operations may be used, such as electron beam welding, brazing, and similar.

A post-weld tempering process maybe performed after step 152. This can increase the strength of the welded joint. Spot tempering may be performed using an induction heater to locally heat the weld, while avoiding heating the cutting teeth to a critical temperature (e.g., about 540 degrees Celsius or about 1000 degrees Fahrenheit) that would soften the cutting teeth and reduce their cutting effectiveness.

The shank may then be affixed to the backing plate and a final finish maybe applied to the entire saw blade. In view of the above, it should be apparent that the techniques of the present invention may provide advantages of increased blade strength, easier

manufacture, and reduced manufacturing time and cost.

While the foregoing provides certain non-limiting example embodiments, it should be understood that combinations, subsets, and variations of the foregoing are contemplated. The monopoly sought is defined by the claims.